Phonographic transducer



July 19, 1949. w. K. RIE BER PHONOGRAPHIC TRANSDUCER Filed Oct. 12, 1945INVENTOR. KM

Patented July 19, 1949 UNITED I STATES PATENT OFFICE PHONOGRAFHICTRANSDUCER William K. Richer, Los, Angeles, Calif. Application October12, 1945, Serial No. 622,061 13 Claims. (01479-10031) My inventionrelates generally to the translating means for converting mechanicalvibration into pulsating or alternating electric current or the reverseof this, converting pulsating or alternating current into mechanicalvibration.

My invention relates more particularly to such translating devices usedin phonographic recording and transcribing equipment of the engraving,or embossing class wherein an undulating groove is embossed or engravedin a moving record medium. I

Several such translating means, which are reversible, are known in theart. Among such reversible means are the variable reluctance magitieticsystem and the piezo-electric crystal sys- In the present embodiment, myinvention is shown employed in an electro-magnetic phonographic tonehead which is adapted for use either asa sound recording head or a soundpick-up head.

For an understanding of my invention, it is well to consider now thefactors and characteristics which should be variable in such a device inorder to adapt it for either of the two above mentioned purposes. Inthis discussion, the following terms will hereafter be used to definethe tone head and its functions: When used as a transducer fortranslating mechanical motion into electrical energy, the device will becalled a pick-up, and when used for the reverse'purpose it will becalled a recording head two functions will be described as playing bacand recording" respectively and the apparatus employing the device willbe referred to as a transcriber and recorder respectively.

Tone heads have been designed which are adaptable for use, both aspick-ups and recording heads, but in all such devices used'previouslythe value of variable factors therein represent compromises between thebest value for recording and the best value for playing back. However,to secure optimum efliciency, it is desirable to change the value of atleast some of such variable factors when changing the function of thedevice from that of recording to that of playing back. Among suchvariable factors in a tone The 2 1 4 the ability of the entire structureto ride the groove or tracki It is desirable that all, or at leastseveral of the factors listed aboveybe automatically andsimultaneouslychanged byv one simple adjust-v ment which thus convertsthe'device from the function of recording to the function of playingback or vice-versa.

- .I have found by experiment that the factors, which it. is mostdesired to change between functions are those of stylus pressure andstiffness and;

my invention deals therefore with-these two var-- iable factors. a

- It is one object of myinvention to provide a sound translating headwhich is adaptable for use as a transducer, either toconvert electricalpulsations into mechanicalyibrations, when used in a recorder, or toperform the reverse of this function when used in a transcriber, Y

It is another object of my invention to provide a sound head of theclass describedin which the mechanical stiffness is dependent on thepressure which is applied to engage an engraving or embossing styluswith a record medium. These and other objects of my invention willappear in 80 rying armature moves in a magnetic field. Such motion ofthe armature results in electric cur rent flow in a pick-up coil or,conversely, current in the coil produces motion of the armature. In theillustrated embodiment, I prefer to use 85 a stretched ligament as aspring for constraining the motion of the armature. In order to changethe mechanical stiffness of the system;

therefore, it is only necessary to increase the tension in the ligament.I provide a lever for this 40 purpose which is so mounted .in the tonehead that when weight is added for the purpose of increasing styluspressure such added Weight also results in increasing the ligamenttension.

For a more detailed description of the tone head embodying my invention,reference should now be had to the attached drawings wherein:

Fig. 1 is an elevational sectional view taken on a vertical plane passedlongitudinally through the center, of the tone head, with the parts inhead of the variable reluctance magnetic type are playback position,

the following: (1) the strength of the permanent magnetic field, (2) themechanical stiffness or spring factor of the moving armature, (3) themechanical damping, (4) the pressure of the re- Fig. 2 is a partiallysectioned the device shown in Fig. 1,

Fig. 3 is an elevational, partially sectioned view taken on the line 3-3in Fig. 1 but with the parts cording stylus against the recordingmedium, (5) in recording position, and

plan view of 5 aeiaesi Fig. 4 is an isometric view of the armatureportion of the device.

Referring now to the above drawings, a casting forms the frame 6 whichsupports the various members of an electromagnetic transducer. Astylus-carrying armature 1 constructed of ferromagnetic material ispivotally supported by the frame 6 in two jewel bearings 8 and 9, one ofwhich 8 is held in an adjustment screw 10. A supportingpivot H ispressed into the annature which is thereby adapted for transverseswingin motion.

A jewel pointed embossing or engraving stylus I2 is supported in thelower end of therarmature and secured therein by a set screw 13.Projecting upwardly from the armature at pivot PI is a blade portion [4of the armature whichiis substantially centrally located in a gap [5between the upper arms of two U-shaped magnetic pole pieces I6 and I1,asibest seen in Fig. 3. The two lower :arm'sof "the magneticpolej-p'ieces HE and I! are brought into a pointadiacent'to fthearmature and near its1piVht H y Magnetic flux :is produced in ime systemby means of a permanent magnet l8 mounted to the back of the frame .6,flux being carried :forward and into the pole pieces l5 :and flbyitwoflux conducting members l9 and 20. Themagnetization of the permanentmagnetic is such was to produce a south pole-in the left hand 130 piece:and a north pole in the right h'and pole piece as best seen in Fig. 3and indicated by the letters N and S.

It will now be seen that as long as the armature l, and hence the bladeportion thereof, remains in a substantially vertical position, as shownin Fig. 3, the magneto-motive forces thereon are balanced and no fluxilows downwardly or upwardly "through the blade portion. However, whenthe stylus is engaged with a moving sound record-andcaused to vibratelaterally thereby, the blade portion 14 of the-armature-will ture blade14 and hence an alternating passes therethrough. This -'alternatingmagnetic flux is converted into alternating electric cur rent by meansof apick-up coil 2| mounted in the frame and between the arms of theU-shaped pole pieces and '50 positioned that the bladeportion 14 of thearmature passes therethroug-h.

Electric leads 38 are broughtout from the coil 2i and may be connectedto'the input of am amplifier for the function of playing back, or theoutput of an amp'lifierforthe function of recording. The method ofmaking such connections is well known in the art and {need not be shownhere.

The process of mechanical, electrical trans: duction performed in thismanner is reversible since alternating current flowing in the coil 2|will produce alternating magnetic flux 'in the blade portion 14 of thearmature, thus causing it to vibrate in the gap 15 and thereby producinglateral vlbrationof the stylus point [2.

in order to maintain the armature 1 .in a sub-,

stantially vertical position, a stretched ligament 22 is provided whichserves as a centeringspring.

stretched rearwardly, passing through .a lon-- gitudinal hole 25 inthearmature "1, and also through a hole 26 in a downwardly projectingportion of the frame. The ligament 22 is secured at its rearward end bypassing through two holes in the lower end of an L-shaped lever member21 and being clamped thereto by a screw 28. The lower end of the lever21 is bent into a U shape and a screw 29 is provided for closing this U,thereby to adjust the initial tension of the ligament 22.

The L-shaped lever 21 is fulcrumedon a blade 30 which in turn is securedto the main frame 6. The top arm of the lever 21 extends forwardly abovethe main frame and in adjustment screw 3! is provided in the main framewhich projects upwardly through a hole in the forward end of the upper'lever arm, as indicated in Fig. 1. Two

nuts .62 ant-1 :33 zare i=provided on this screw, one

32 below and one 33 above the lever arm 21. The

'nuts "32 and 33 form upper and lower stops, thus the ho'le'25 in-themain frame 6.

Two lateral downwardly projecting arms 35 and'36 are provided onthrearward end of the main frame 6, and have journal bearings in thelower ends thereof, thereby to mount the'entire structure for verticalswinging motion above a moving record medium.

The device described is adapted for the dual purpose of recording andplaying back and 0perates as follows: In the condition shown in Fig. 1;the tone head is adapted to function *as "a pickup, that is, =when=the-stylus l 2 *is engagedwith an undulatinggroove in a moving 'recordfthelateral vibration of the stylus and hence the armature 1 produces"correspondingly plusating electric current in thecoil 2'! Now toconvertthe tone liead-for' th'e function of recording, pressure is applied at apoint indicated 'by the numeral 31 in Fig. 1, as for example by-th'eaddition of a weight 3l thereat as shown in Fig.3 or by a downwardlythrusting spring.

The added down-ward pressure first moves the upper arm of the-lever Z'ldowri-wi'rrdlyagain-st the lower adjustingnut 32 thus *rotating thelever counterclockwise-about the "fulcrum 30 and mcreasingthe-tension-in=the 1igame1'it 22. The in- 1 recordmediumv for the ipuipose 0f embossing or engravingn groove therein. JDuringthe recordingfunction, relatively vgreater magnetic flux strength must beaprcducedlin the ibladenportion IA of the warmature ..than .during theplay-back funct on, :since during IECDId-ing, :it is necessary to deformthe record medium. Greater magnetic flux strength in the armature .tendsto, produce greater lateral excursions thereof :during which thearmature bladel'd would tend to strike the pole pieces 15 and III. Thisatendencyais .overcome in thepresent pmbodiment by the aforementionedincreased :stifiness .during the recording function.

The armature .I and stretched ligament 22 if undamped would form anoscillating system in which sustained vibration would be possible andwhich would be alinear in its response to varying frequencies ofalternating current in the coil 2|. In order to preventsuch :resonanceinthe. armature system, the .damping sleeve 34 is provided which is soproportioned andof energy absorbing material such as to critically dampthe armature motion. U i i a It will be seen by those skilled in the artthat it is the essence of my invention to provide in a phonographictransducer, a mechanical oscillator,..the compliance factor of which isvaried between the functions of recording and playing back and to soconstruct the transducer that. the stiffness of the variable complianceis increased automatically when additional stylus pressureisproduced..., Various alternate methods.- of embodying my invention willbe apparent and I do not mean to be limited to the embodiment disclosedherein but rather to the scope of the appended claims.

I claim:

1. In a dual purpose phonographic transducer: a supporting frame; astylus carrying ferro-magnetic armature, pivotally mounted in said framefor laterally swinging motion therein; a stretched ligament connectingsaid armature to said frame and constraining said swinging motion; adamping sleeve of energy absorbing material surrounding said stretchedligament; a lever fulcrumed in said frame and moving in response torecord engaging pressure of a stylus carried by said armature, one endof said lever being connected to said ligament whereby said styluspressure responsive motion results in corresponding variation in saidligament tension; means for producing a permanent magnetic fieldsurrounding said armature such that laterally swinging motion isaccompanied by alternating magnetic flux flow in a portion of saidarmature; a coil surrounding said alternating magnetic flux-carryingarmature portion, said coil so connected that current flow therein isaccompanied by corresponding magnetic flux flow in said armatureportion; and means for selectively connecting said coil to a source ofalternating electric current or to a means for detecting such current.

2. In a dual purpose transducer: a supporting frame; an armature movablymounted in said frame; a spring connecting said armature and frame andunder initial tension to constrain said armature movement; a movablemember in said frame connected to said spring; means to selectivelydetect or produce mechanical vibration in said armature; an element insaid armature adapted to selectively produce a sound record in a movingsound recording medium engaged therewith or to vibrate said armature inresponse to a moving sound record engaged thereto; and means toselectively apply pressure to said movable memher to move the samewhereby to increase the tension in said spring and simultaneouslyincrease pressure of engagement of said element.

3. In a dual purpose transducer: a supporting frame; an armature movablymounted in said frame; a spring constraining motion of said armature;stylus means to selectively engage said armature with a source ofmechanical vibrations or with a medium for recording such vibrations; amovable member in said frame connected to said spring; and means toselectively apply pressure to said member whereby to simultaneouslyincrease tension in said spring and apply medium engaging pressure tosaid armature.

4. In a dual purpose transducer: a supporting frame; an armature movablymounted in said frame; stylus means to selectively engage saidarmaturewith a sourceof. mechanical vibrations or with a medium forrecording such vibrations; movable means insaid frame resilientlyconnected to said armature; and means to-selectively apply pressure tosaid movable means whereby to simultaneously decrease the mechanicalcompliance of said armature and apply medium engaging pressure to saidstylus means. I

5. In a dual purpose transducer: a supporting frame; an armaturemovably'mounted in said frame; a spring connecting'said armature andframe and under initial tension to constrain said armature movement; amovable member in said frame connected to said spring; means toselectively detect or produce mechanical vibration in said armature; anelement in said armature adapted to selectively produce a sound recordin a moving sound recording medium engaged therewith or to vibrate saidarmature in response to a moving sound record engaged thereto; means toselectively apply pressure to said movable member to move the samewhereby to increase the tension in said spring and simultaneouslyincrease pressure of engagement of said element; and adjustable meansfor limitin the motion of said movable means whereby to adjust theamount by which said spring tension is increased by said movable means.

6. In a dual purpose transducer: a supporting frame; an armature movablymounted in said frame; a spring constraining motion of said armature;stylus means to selectively engage said armature with a source ofmechanical Vibrations or with a medium for recording such vibrations; amovable member in said frame connected to said spring; means toselectively apply pressure to said member whereby to simultaneouslyincrease tension in said spring and apply medium engaging pressure tosaid armature; and adjustable means for limiting the motion of saidmovable means whereby to adjust the amount by which said spring tensionis increased by said movable means.

7. In a dual purpose transducer: a supporting frame; an armature movablymounted in said frame; stylus means to selectively engage said armaturewith a source of mechanical vibrations or with a medium for recordingsuch vibrations; movable means in said frame resiliently connected tosaid armature; means to selectively apply pressure to said movable meanswhereby to simultaneously decrease the mechanical compliance of saidarmature and apply medium engaging pressure to said armature; andadjustable means for limiting the motion of said movable means wherebyto adjust the amount by which said compliance is changed.

8. In a dual purpose transducer: a supporting frame having alignedbearings therein; a vibratory member pivctally mounted in said bearings;means in said frame to selectively vibrate or detect vibration in saidvibratory member; stylus means fixed to said vibratory member andadapted to engage the same selectively with an external source ofmechanical vibration or with a medium for recording such vibration; acompliance control member movably mounted in said frame; a pre-stressedspring connected between said control member and vibratory member andadapted to resist movement of said vibratory member; and meanspositioned and adapted to apply pressure to said compliance controlmember and frame whereby to increase the medium-engaging pressure ofsaid stylus means and simultaneously to increase the resistance of ,Saidspring.

57$ 1 a 9 The construction oi claim. 8 WM mztlmt: me tenizedthat'sai'd-i l'szst named meansincludes a, aleven fulcmmedz'imsaidweight afiapteef tureshon ccmfirol' memirem 11 159*. Thecans-tructlon ofalarm & fm'fiher char-- 7 (ms acfierized? byhaving adfiustabl'eabutment? mm 61 bers in said frame; positioned and adaptedto li'n'r- Thefollowing refmtenlces are of record in the it the movement ofsai'cfcontrol member; We of this patfemir 11. The construction ofclaim gmrthercharacmm ST terizedj'inthat said sprihgis afiensioned ligament w V 1'2.The construction efclaimii further chamzm- Name W terizerL by having a.body ofenergy-ahsorb'ing mai f; terial engaged withsaidvibratuxymembenwher;& 3 f; 15 i 'm 1932; by damp thesame" 211mm EeMacIaiIer- Sepia-1231939 Theconstmctim (if hereha ab x 2,318,398 1 1

